Preparation of solid organoboron fuels



United States Patent 3,316,307 PREPARATION OF SOLID ORGANOBORON FUELS Perry R. Kippur, Hamden, Conn., assignor, by mesne assignments, to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Jan. 3, 1957, Ser. No. 632,397 3 Claims. (CL 260-6065) This invention rel-ates to fuels and, more particularly, to solid organoboron fuels obtained by the reaction of diborane and acetylene.

The fuels of this invention, when incorporated with suitable oxidizers such as ammonium perchlorate, potassium perchlorate, sodium perchlorate, ammonium nitrate, etc., yield solid propellants suitable for rocket power plants and other jet propelled devices. Such propellants burn with high flame speeds, have high heats of combustion and are of the high specific impulse type. Probably the single most important factor in determining the performance of a propellant charge is the specific impulse; appreciable increases in performance will result from the use of ln'gher specific impulse materials. The fuels of this invention when incorporated with oxidizers are capable of being formed into a wide variety of grains, tablets, and shapes, all with desirable mechanical and chemical properties. Propellants produced by the methods described in this application burn uniformly without disintegration when ignited 'by conventional means, such as a pyrotechnic igniter, and are mechanically strong enough to withstand ordinary handling.

In accordance with this invention, fuels which are solid addition products of diborane and acetylene are prepared by reacting diborane and acetylene while the diborane is dissolved in tetrahydrofuran. The tetrahydrofuran used is preferably as dry as possible, inasmuch as this tends to increase the yield of the solid reaction product of the diborane and acetylene. The reaction temperature utilized can be varied widely, generally being from C. to 100 C., and preferably from 20 C. to 75 C. Likewise, the reaction time can be varied, generally being Within the range from 20 minutes to five hours, and preferably from one hour to two hours. If desired, methyl acetylene or mixtures of acetylene and methyl acetylene can be utilized in place of acetylene and solvents other that tetrahydrofuran can be employed, for example, lowerv dialkyl ethers containing from one to four carbon atoms in each alkyl radical such as dimethyl ether, methylethyl ether, diethyl ether, methyl n-propyl ether, diisopropyl ether, and the like.

The following examples illustrate various embodiments falling Within the scope of this invention.

EXAMPLE I In this experiment 100 ml. of anhydrous tetrahydrofuran was placed in a reaction flask equipped with a condenser cooled to -78 C. The system was purged with nitrogen for /2 hour before the reaction was begun. Diborane gas was passed into the tetrahydrofuran at a rate of 100 ml. per minute at S.T.P. for one hour. This is slightly more than necessary to saturate the tetrahydrofuran at 20 C. The acetylene gas was then passed in at the same rate, 100 ml. per minute at S.T.P., for /2 hour. The reaction was exothermic and the temperature gradually rose to approximately 40 C. Twenty minutes after the start of the acetylene flow the mixture became turbid and a precipitation of a white solid began. After one hour the reaction was terminated by stopping the flow of the acetylene into the tetrahydrofuran. The system was purged with nitrogen for /2 hour and the White solid was filtered from the tetrahydrofuran under a nitrogen atmosphere with a small amount of pressure.

This white solid was dried under vacuum for one hour and traces of ether were removed under reduced pressure. Care was taken to keep oxygen and moisture away from the solid. The vacuum dried white solid weighed 3.7 grams. The solid was pyrophoric in air after vacuum drying and reacted slowly with water and vigorously with methanol.

An elemental analysis showed that the white solid contained 57.2 weight percent carbon, 17.8 weight percent hydrogen and 24.6 weight percent boron. The solid produced 1.1 to 1.4 molecules of hydrogen per atom of boron present in the solid upon treatment with methanol.

EXAMPLE II The tetrahydrofuran used in this example was dried with anhydrous calcium chloride for 24 hours to remove any excess water and/or alcohol. Then it was decanted into a distilling flask and treated with sodium hydride in a nitrogen atmosphere until a blue color appeared momentarily. The material then was refluxed for 20 minutes, then distilled slowly through a 5 plate helix was purged with nitrogen for 10 minutes, acetylene gas then was passed into the tetrahydrofuran solution containing diborane at a rate of 200 ml. per minute at S.T.P. for about 30 minutes. The temperature rose to 67 C. in the first 10 minutes. Twelve minutes after the flow of acetylene was started a white precipitate formed. The flow of acetylene was continued for about 20 minutes. The system was purged with nitrogen for /2 hour. The White solid was separated from the tetrahydrofuran and treated in the same manner as in Example I.

An elemental analysis showed that the white solid contained 28.2 (28.0, 28.3) weight percent boron.

EXAMPLE III Seventy-five milliliters of pure tetrahydrofuran was placed in a 200 ml. flask equipped with a gas dispersion tube and a Dry-Ice cooled condenser. The system was flushed with nitrogen, and the diborane gas then was passed through at a rate of 250 ml. per minute at S.T.P. Considerable heating was observed. Solid ice-like droplets formed on the Dry-Ice cooled condenser. Diborane was added for a total of 30 minutes. The final temperature was 30 C. Acetylene gas then was added at the same rate for a total of fifteen minutes. After the first 10 minutes a white precipitate began to form. A Cloud zone was observed above the liquid. At first the reaction was mild with slight heating, but after a few moments the mixture remained practically at reflux by its own heating. After the 15 minute treatment with acetylene, the mixture was arranged for reflux and then diborane was bubbled through at 250' mL/minute for fifteen minutes. The mixture was cooled to room temperature and flushed with nitrogen. The precipitated solid was filtered under nitrogen and dried under vacuum.

The boron-containing solid materials produced by practicing the method of this invention can be employed as ingredients of solid propellant compositions in accordance with general procedures which are well-understood in the art, inasmuch as the solids produced by practicing the present process are readily oxidized using conventional solid oxidizers, such as ammonium perchlorate, potassium perchlorate, sodium perchlorate, ammonium nitrate and the like. In formulating a solid propellant composition employing one of the materials produced in accordance with the present invention, generally from 10 to 35 parts by weight of boron-containing material and from 65 to 90 parts by weight of oxidizer, such as ammonium perchlorate, are present in the final propellant composition. In the propellant, the oxidizer and the product of the present process are formulated in intimate admixture with each other, as by finely subdividing each of the materials separately and thereafter intimately admixing them. The purpose in doing this, as the art is aware, is to provide proper burning characteristics in the final propellant. In addition to the oxidizer and the oxidizable material, the final propellant can also contain an artificial resin, generally of the urea-formaldehyde or phenol-formaldehyde, type, the function of the resin being to give the propellant mechanical strength and at the same time improve its burning characteristics. Thus, in manufacturing a suitable propellant, proper proportions of finely divided oxidizer and finely divided boron-containing material can be admixed with a high solids content solution of a partially condensed ureaformaldehyde or phenol-formaldehyde resin, the proportions being such that the amount of the resin is about 5 to percent by weight, based upon the weight of the oxidizer and boron compound. The ingredients are thoroughly mixed with simultaneous removal of the solvent, and following this the solvent-free mixture is molded into the desired shape, as by extrusion. Thereafter, the resin can be cured by resorting to heating at moderate temperatures. For further information concering the formulation of solid propellant compositions, reference is made to U.S. Patent No. 2,622,277 to Bonnell et al. and U.S. Patent No. 2,646,596 to Thomas et al.

It is claimed: 1. A method for the preparation of a solid reaction product of diborane and acetylene which comprises reacting diborane and acetylene at a temperature Within the range from 10 C. to 100 C. while the diborane is dissolved in tetrahydrofuran.

2. The method of claim 1 wherein the reaction is conducted at a temperature within the range from 20 C. to C.

3. In the process for preparing an or'ganoboron compound by the reaction of diborane with an unsaturated organic compound selected from the group consisting of acetylene and methylacetylene, the improvement which includes conducting said reaction in a liquid phase and in the presence of a compound selected from the group consisting of tetrahydrofuran and lower dialkyl ethers.

References Cited by the Examiner U NITED STATES PATENTS 1,888,713 11/1932 Britton et a1. 23-1 OTHER REFERENCES Elliott et al., American Chem. Soc. Jour., vol. 74 (1952), pages 5211 to 5212.

Stock, Hydrides of Boron and Silicon, Cornell University Press, Ithaca, N.Y., 1933, page 150.

Stock and Kuss, Ber. Deut. Chem., vol. 56, page 808, (1923).

TOBIAS E. LEVOW, Primary Examiner.

LEON D. ROSDOL, R. L. CAMPBELL, WILLIAM G.

WILES, Examiners.

L. A. SEBASTIAN, W. F. W. BELLAMY,

Assistant Examiners. 

1. A METHOD FOR THE PREPARATION OF A SOLID REACTION PRODUCT OF DIBORANE AND ACETYLENE WHICH COMPRISES REACTING DIBORANE AND ACETYLENE AT A TEMPERATURE WITHIN THE RANGE FROM 10*C. TO 100*C. WHILE THE DIBORANE IS DISSOLVED IN TETRAHYDROFURAN. 